The Auditory System

The auditory system is one of the human body’s most complex and delicate sensory systems.

Hearing begins when the outer ear, the visible portion that is on the outside of the head (known as the pinna), channels sound waves into the external auditory canal. This tube-like passageway is lined with tiny hairs and small glands that produce ear wax (cerumen). The shape of the external ear works to collect and amplify sound waves.

The middle ear lies at the end of the auditory canal. It is composed of the tympanic membrane (ear drum) and three of the smallest bones in the body named for their shapes – the hammer (malleus), anvil (incus), and stirrup (stapes). When sound waves hit the ear drum, it vibrates and in turn, moves the hammer. This mechanical energy is transferred through these bones into the inner ear.

The inner ear is completely contained within the temporal bone of the skull and is filled with nerves, receptors and fluids. The cochlea receives sound waves from the middle ear and transforms the energy into fluid motion, which disturbs sensory cells that line the coiled cochlea. Movement of these hair-like sensory cells triggers activity in hearing nerve fibers that fire electrical messages to the part of the brain responsible for interpreting sound. The auditory cortex is an area on each side of the brain responsible for interpreting the sounds we hear. The entire process occurs within a split-second timeframe.

The inner ear also contains three semi-circular canals that help us maintain our sense of balance.

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